Podostemaceae Rich. ex C.A. Agardh
Including Marathrinae (Marathraceae) Dum., Tristichaceae Willis, Philocrenaceae Bong.
Habit and leaf form. Aquatic herbs. Plants of very peculiar vegetative form; more or less thalloid (lichenoid or seaweed-like, or ‘bryophytic’). Leaves well developed (but minute, on secondary shoots, without axillary buds), or much reduced, or absent. Plants rootless (attached by ‘haptera’). Annual (often), or perennial. Hydrophytic; rooted (growing on rocks in rivers or cataracts). Leaves when present, minute; alternate; imbricate; sessile; non-sheathing; simple, or compound; sometimes much dissected.
Stem anatomy. Nodes unilacunar. Secondary thickening absent (vascular tissue greatly reduced). Xylem without vessels.
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; in cymes. The terminal inflorescence unit when flowers aggregated, cymose. Inflorescences cymes, often spiciform; spatheate (in Podostemoideae, the spathes enclosing up to twenty flowers). Flowers bracteolate; small; regular to very irregular (dorsiventrally flattened to varying degrees); cyclic; tricyclic to polycyclic.
Perianth sepaline, or petaline, or vestigial; when present, 1, or 2–3(–5), or 5–50 (to ‘many’); free, or joined; 1 whorled.
Androecium 1, or 2–100 (to ‘many’). Androecial members free of the perianth; coherent (usually with basally connate filaments), or free of one another; 1–5 whorled (? — to ‘several’ whorled). Androecium exclusively of fertile stamens. Stamens 1–30. Anthers tetrasporangiate (usually with the microsporangia aligned in a row). Endothecium developing fibrous thickenings. Microsporogenesis successive, or simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Tapetum glandular. Pollen shed in aggregates, or shed as single grains; when aggregated, in diads. Pollen grains aperturate (usually), or nonaperturate (occasionally); when aperturate, 3 aperturate, or 4–9 aperturate (rarely); colpate, or colporate, or foraminate (rarely); 2-celled.
Gynoecium (1–)2(–3) carpelled. The pistil (1–)2(–3) celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary (1–)2(–3) locular. Styles (1–)2(–3); partially joined; apical. Placentation when unilocular, free central; when 2(–3)-locular, axile. Ovules 2–50 per locule (to ‘many’); anatropous; bitegmic; tenuinucellate. Outer integument contributing to the micropyle. Embryo-sac development reduced Allium-type (with variations on this). Embryogeny solanad.
Fruit non-fleshy; dehiscent; a capsule. Seeds non-endospermic (there being no double fertilization); small. Cotyledons 2. Embryo straight.
Seedling. Germination phanerocotylar.
Physiology, biochemistry. Aluminium accumulation not found.
Geography, cytology. Sub-tropical to tropical. Pantropical and warm North America. X = 10.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Podostemiflorae; Podostemales. Cronquist’s Subclass Rosidae; Podostemales. APG (1998) Eudicot; core Eudicot; Rosid; unassigned to Eurosid I or Eurosid II; unassigned to order. Species 130. Genera 48; Angolaea, Apinagia, Butumia, Castelnavia, Ceratolacis, Cladopus, Crenias, Crenias, Dalzellia, Devillea, Dicraeanthus, Diplobryum, Djinga, Endocaulos, Farmeria, Hydrobryopsis, Hydrobryum, Indotristicha, Jenmaniella, Lawia, Ledermanniella, Leiothylax, Letestuella, Lonchostephus, Lophogyne, Macrarenia, Macropodiella, Malaccotristicha, Marathrum, Monostylis, Mourera, Oserya, Paleodicraeia, Podostemum, Polypleurella, Polypleurum, Rhyncholacis, Saxicolella, Sphaerothylax, Stonesia, Thelethylax, Torrenticola, Tristicha, Tulasneantha, Weddellina, Willisia, Winklerella, Zehnderia, Zeylandium.
Illustrations. • Technical details (Tristicha).
Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. http://biodiversity.uno.edu/delta/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).
